Method for the production of organic fertilizer based on ammonium and/or nitrate

Abstract

Method for the production of organic fertilizer comprising providing an organic source of ammonia gas, in particular air contaminated with ammonia gas, directing the air contaminated with ammonia gas through water and forming an ammonium hydroxide solution converting the ammonium into nitrate, dosing, under the control of a control system, the ammonium hydroxide solution to a recirculation stream from a second bio-reactor with bacteria suitable for converting the supplied ammonia into nitrite and nitrate. The amount of ammonium water fed by the control system to the acidic nitrate solution from the second bio-reactor depends on one or more measured pH values in the device.

Claims

1. Method for the production of organic fertilizer or organic raw material for, inter alia, the manufacture of yeast, based on ammonium and/or nitrate, comprising the steps of: providing an organic source of ammonia gas; dissolving the ammonia gas in water to form an NH.sub.3 solution in water; oxidizing ammonium hydroxide in the NH.sub.3 solution in water with air to nitrite by means of bacteria, and then oxidizing the nitrite with air to nitrate by means of bacteria to form an acidic nitrate solution, characterized, in that the method comprises the steps: producing an acidic nitrate solution in a first bio-reactor by means of bacteria; discharging the acidic nitrate solution from the first bio-reactor to a second bio-reactor for further conversion of nitrite to nitrate by means of bacteria; maintaining an O.sub.2 saturation of at least 80% at the prevailing temperature in the first bio-reactor and the second bio-reactor; recirculating the content from the second bio-reactor to the first bin-reactor as an acidic nitrate solution recirculation stream; wherein an NH.sub.3 solution in water is dosed into the acidic nitrate solution recirculation stream to form a feed stream of the first bio-reactor having a greater than 6, said feed stream being supplied to the first bio-reactor, wherein the amount of NH.sub.3 solution in water suppled to the acidic nitrate solution recirculation stream is controlled by a control system dependent on the measured pH value of the acidic nitrate solution recycle stream and/or the measured pH value in the feed stream; disconnecting the first bio-reactor and the second bin-reactor; and discharging the nitrate solution of the second bio-reactor.

2. Method according to claim 1, wherein the acidic nitrate solution from the second bio-reactor is recirculated repeatedly until the nitrate concentration is between 2 and 25% by weight in the second bio-reactor.

3. Method according to claim 1, wherein the desired pH value of the feed stream controlled by the control system is in the range of 6.5-7.3.

4. Method according to claim 1, wherein the NH.sub.3 solution in water is fed to the acidic nitrate solution of the second bio-reactor to form an ammonium nitrate solution.

5. Method according to claim 1, wherein the first bio-reactor comprises surface expanders on which allow the bacteria grows.

6. Method according to claim 5, wherein the first bio-reactor comprises mixing baffles being arranged to cause the feed stream, fed to the first bio-reactor, to pass through the first bio-reactor, and flow out form the discharge location of the first bio-reactor.

Description

(1) Hereinafter the invention will be discussed in more detail with reference to an embodiment, with reference to a FIGURE.

(2) FIG. 1 shows an embodiment of a device for converting NH.sub.3 to nitric acid and/or to ammonium nitrate.

EXAMPLE

(3) FIG. 1 shows a flowchart of a device according to the invention for carrying out the method according to the invention.

(4) In this example, the NH.sub.3 to be converted to the bio-nitrate fertilizer is supplied by a tank truck 1 as a NH.sub.3 solution in water 2.

(5) The composition of the NH.sub.3 solution in water 2 is determined by the following equilibria:
NH.sub.3(g)+H.sub.2O(l)<->NH.sub.3(aq)+H.sub.2O(l)<->NH.sub.4+(aq)+OH.sup.−(aq)

(6) The NH.sub.3 solution in water 2 is basic (alkaline) with a pH>7 due to the formation of OH.sup.− during the dissolution of NH.sub.3.

(7) By means of a NH.sub.3 dosing device 3, the NH.sub.3 solution in water 2 is dosed into the recirculation stream 4 from the second bio-reactor 6 to the first bio-reactor 5. The recirculation stream 4 is maintained by a recirculation pump 7. The first bio-reactor 5 is a vessel with preferably a conical bottom in which a mixture is present of some ammonia-oxidizing bacteria including Proteobacteria, Nitrosomonas and Nitrosococcus. In this example, the second bio-reactor 6 is a vessel of the same size as the first bio-reactor 5. The first and second bio-reactors are aerated with air 10 (or oxygen) from an aerating unit 11 to an O.sub.2 saturation of at least 80% at the prevailing temperature. The oxygen concentration in the first and second bio-reactor is measured with oxygen meters.

(8) The liquid content of the first and second bio-reactor 5, 6 is heated to a temperature of approximately 28° C. Under these conditions, the ammonia-oxidizing bacteria will oxidize the ammonium hydroxide with oxygen to nitrite according to the following overall reaction equation.
NH.sub.4+(aq)+OH.sup.−(aq)+1.5O.sub.2(g)->NO.sub.2.sup.−(aq)+H.sup.+(aq)+2H.sub.2O(l)

(9) In a second reaction step, the nitrite formed is oxidized with oxygen to nitrate by nitrite-oxidizing bacteria according to the reaction equation:
NO.sub.2.sup.−(aq)+H.sup.+(aq)+0.5O.sub.2(g)->NO.sub.3.sup.−(aq)+H.sup.+(aq)

(10) Oxidation of nitrite to nitrate is carried out by nitrite-oxidizing bacteria including Nitrobacter and Nitrospira. As a result, the basic (alkaline) feed of NH.sub.3 solution in water 2 is converted into an acidic nitrate solution 8 (nitric acid) having a pH <7. This acidic nitrate solution 8 flows to the second bio-reactor 6, where the conversion of nitrite to nitrate further continues, although the pH rises quickly and is often too high for the nitrite-oxidizing bacteria.

(11) Subsequently, the content of the second bio-reactor 6 is recirculated to the first bio-reactor 5 by means of the recirculation stream 4 provided by recirculation pump 7. In this recirculation stream 4 the pH is measured and on the basis of the pH measurement the NH.sub.3 dosing device 3 doses a corresponding amount of basic NH.sub.3 solution in water 2, so that a pH >7 is obtained with the solution of the formed feed stream 9 and as a result all nitric acid from the second bio-reactor is converted to ammonium nitrate.
NH.sub.4.sup.+(aq)+OH.sup.−(aq)+NO.sub.3.sup.−(aq)+H.sup.+(aq)->NH.sub.4.sup.+(aq)+NO.sub.3.sup.−(aq)+H.sub.2O(l)

(12) The ammonia-oxidizing bacteria in the first bio-reactor 5 convert the ammonium nitrate to nitrite according to the following overall reaction equation:
NH.sub.4.sup.+(aq)+NO.sub.3.sup.−(aq)+1.5O.sub.2(g)->NO.sub.2.sup.−(aq)+2H.sup.+(aq)+NO.sub.3.sup.−(aq)+H.sub.2O(l)

(13) In a second step, the nitrite formed is converted to nitrate according to the reaction equation:
NO.sub.3.sup.−(aq)+NO.sub.2.sup.−(aq)+2H.sup.+(aq)+0.5O.sub.2(g)->2NO.sub.3.sup.−(aq)+2H.sup.+(aq)

(14) From the above reaction equations, it is clear that the concentration of HNO.sub.3 (nitric acid) has doubled in the effluent of the first bio-rector after the first recirculation. Here, for convenience, the small dilution by the water formed is not taken into account in the oxidation of NH.sub.4.sup.+ (aq). As a result, the nitrate concentration in the second bio-reactor 6 will increase over time.

(15) During the next recirculation of the second bio-reactor to the first bio-reactor, the concentration of nitrate will increase again. The unit is operated for a predetermined period of time, and the nitric acid/ammonium nitrate mixture in the second bio-reactor is recirculated for a predetermined period of time, resulting in a nitrate concentration of 10 wt. % or more in water. With this method, it is possible to obtain nitrate concentrations in the second bio-rector between 2 and 25% by weight. This product is suitable for use as organic fertilizer or organic raw material.

(16) In a next step, the first bio-reactor 5 and the second bio-reactor 6 are disconnected from each other and optionally the acidic nitrate product in the second bio-reactor is made basic or pH neutral by forming ammonium nitrate with the NH.sub.3 solution in water 2 according to the reaction equation:
NH.sub.4.sup.+(aq)+OH.sup.−(aq)+NO.sub.3.sup.−(aq)+H.sup.+(aq)->NH.sub.4.sup.+(aq)+NO.sub.3.sup.−(aq)+H.sub.2O(l)

(17) It is also possible to increase the concentration of nitric acid and/or ammonium nitrate by evaporation or otherwise removing the solvent water.

(18) The nitrate solution in the second bio-reactor 6 is then discharged to the final product filling plant 13 or to, for example, a tank truck for transport to a packaging unit.

(19) When a third bio-reactor 12 is added to the device (unit) for carrying out the method according to the invention, the device can be operated continuously. The third bio-reactor 12 is configured in parallel with the second bio-reactor, so that the acidic nitrate solution 8 can flow from the first bio-reactor 5 to the third bio-reactor 12 and recirculate to the first bio-reactor 5, while the produced nitrate solution in the second bio-reactor 6 is discharged, for example to the final product filling plant 13.